1. Field of the Invention
The resent invention relates to an overall structure and an optimum operation range of a sealed scroll compressor for helium.
2. Description of the Related Art
A well known example of the related art of a scroll compressor for helium is described in Japanese Patent Application Laid-Open No. 2002-89469 (hereinafter referred to as JP-2002-89469-A). Described in JP-2002-89469-A is that: in order to obtain a sealed scroll compressor for helium capable of stably operating under a range of very small pressure ratio without deteriorating the efficiency, the distal end portion (portion shown in a dashed line) of a scroll wrap for air conditioning is cut so as to obtain a tooth shape of a scroll wrap having a smooth arc 66 with a radius of R1 connecting point A and point C. The point A is an initial point of an involute curve 65. Curve 68 is also an involute curve. Point D and point C is connected with an arc with a radius of R3. In this configuration, a fixed scroll and a orbiting scroll have a scroll tooth shape with a set volume ratio Vr of 1.8 to 2.3 in the scroll wrap portion (See Abstract).
In JP-2002-89469-A, an exemplary structure of a sealed scroll compressor for helium including an oil injection mechanism part, for cooling a helium working gas, connected to an oil injection port provided on an end plate of a fixed scroll via an oil injection tube penetrating a sealed container, is described. It is also described that the set volume ratio Vr (Vth/Vd, i.e., a ratio of a stroke volume Vth which is a maximum suction volume to a volume Vd which is a volume of an innermost chamber) of a compression chamber formed by a fixed scroll side and a orbiting scroll side is around 2.1 and that the operation pressure is from a standard condition to the maximum suction pressure condition which is about 0.6 MPaG to 1.0 MPaG or smaller.
In such related art, obtainable flow rate of helium gas may be limited. And under an operation condition in which the operation pressure ratio Pd/Ps (ratio of a discharge pressure Pd to a suction pressure Ps) may be as small as from 1.5 to 1.7, due to a notable decrease in a flow rate of an injection oil for cooling, sealability inside the compression chamber may be deteriorated which may result in a rise in a compressor input and a notable reduction in volumetric efficiency.